Two-cycle engine idling speed limiter



Feb. 13, 1962 w. B. BURKETT TWO-CYCLE ENGINE IDLING SPEED LIMITER 2SheetsSheet 1 Filed Aug. 19, 1959 r n R." w M M 0 r h w.

Feb. 13, 1962 w. B. BURKETT 3,020,777

TWO-CYCLE ENGINE IDLING SPEED LIMITER Filed Aug. 19, 1959 2 Sheets-Sheet2 INVENTOR.

Wu. FORD B. Bum r hzhzza z lrroausra United States atet 3,020,777Patented Feb. 13, 1962 3,020,777 TWO-CYCLE ENGINE IDLING SPEED LllVlITERWilford B. Burkett, Minneapolis, Minn., assignor to Me- CullochCorporation, Marine Products Division, Minneapolis, Minn., a corporationof Minnesota Filed Aug. 19, 1959, Ser. No. 834,740 7 Claims. (Cl.74-472) This invention relates to a speed control for limiting theno-load idling speed of a two-cycle internal combustion engine.

- The speed of two-cycle internal combustion engines is usuallycontrolled by retarding and advancing the ignition and controlling thefuel mixture intake. When used in outboard motors these engines areconnected to the propeller by clutches and manually shiftable gears suchas described by D. A. Armstrong et al., Patent No. 2,653,- 277, issuedDecember 22, 1953, the operation of which is described beginning at line17 of column 7. It may be noted that the motor has a neutral positionwherein the two-cycle engine is effectively disconnected from thepropeller and thus in a no-load condition.

In two cycle engines, particularly the larger ngines, there is atendency for the engine during no-load conditions to maintain increasedengine speeds at a dangerous and harmful level regardless of the sparkand fuel mixture adjustments. This speed runaway is believed caused byback breathing through the exhaust ports providing insufiicientscavenging of diluted fuel mixture in the combustion chamber. Everyseveral cycles a combustion charge is accumulated to keep the enginerunning at increased speeds.

Previously the increased speed has been prevented by sensing the vacuumin the intake manifold and using high manifold vacuum as a criterion forshorting the ignition to ground and thus preventing the excessive speed.It has been noted that the pressure variation in the intake manifold wasslight, the total pressures being measured in inches of water column.This absolute pressure variation is also dependent on the carburetoradjustments and therefore subject to variations with respect to trueengine s eed.

This invention provides two-cycle engine idling speed controls in whichthe control is stably related to true engine speeds regardless of engineadjustments. Additionally control means are provided in which the enginespeed is limited to the desired idling speed even when the actual sparkor fuel mixture adjustment are adjusted as to provide an engine speedgreater than the desired speed. According to this invention a pressuresensitive switch is operatively connected to the coolant system whichprovides a high pressure proportionately related to engine speed for useas a criterion in making the ignition system ineffective to produce aspark. Additionally an interlock switch is provided on the gear shift orclutch lever making the pressure sensitive switch electrically operativeonly during periods of engine no-load conditions.

These and other more detailed and specific objects will be disclosed inthe course of the following specification, reference being had to theaccompanying drawings, in which:

FIG. 1 is a vertical axial sectional view through an outboard motorembodying the invention.

FIG. 2 is a sectional view of an engine block installed pressureresponsive switch together with a schematic diagram of the idling speedcontrols for use in a battery operated two-cycle engine.

FIG. 2A is a modification of the FIG. 2 circuit.

FIG. 3 is a schematic diagram of an idling speed control for use with amagneto operated two-cycle engine.

FIG. 4 is a schematic diagram of an idling speed control for use with anoutboard motor having magneto operated individual ignition systems foreach cylinder.

With more particular reference now to the drawing like numbers denotelike parts and structural features in the views and various schematicdiagrams. In FIG. 1 there is shown an outboard motor having a power head10 with a two cylinder two-cycle internal combustion engine 12 therein.The engine 12 has a vertical drive shaft 14 gearingly driving the usualpropeller 16. On the forward side of the vertical housing 18 there is awater or coolant intake 20 coupled to water or coolant pump 22 driven bythe shaft 14 for pumping Water from a boat supporting body of water (notshown) through a tube 23 to the engine block 24 for cooling same. Thewater coolant leaves the block 24 through restricted outlet tube 25 intothe exhaust system of the motor. Since pump 22 is directly driven by theshaft 14 on the engine side of the clutch generally designated bynumeral 26, the water or coolant pressure in block 24 is proportionatelyrelated to the engine r.p.m. or speed and provides up to 8-10 p.s.i.water pressures.

In power head 10 an ignition system 28, of either the battery or magnetotype, provides timed electric spark to spark plugs 30 and 31 forigniting the fuel mixture in the engine cylinders. Also the usual gearshift lever 32 provides control over the gear shifting structure ofArmstrong et al., supra, and has a forward, neutral and reversepositions respectively indicated by dotted lines 32, 32 and 32.

The improvements provided by this ignition include a cam element 34attached to gear shift 32 and disposed with relation to spring loadedswitch 36 to actuate same when the gear shift is in the neutral position32 and permitting the switch to return to its spring urged normalposition as will be more fully described. It may therefore be seen thatswitch 36 will be actuated when the gear shift 32 is in a neutralposition.

Switch 36 is electrically connected to a pressure responsive switch 38in an ignition system controlling conjunctive circuit relation. That is,both switches 36 and 38 are actuated to effect the desired control overignition system 28. This is more easily understood with reference toFIG. 2 wherein switch 38 comprises a threaded nipple 40 screwed into anengine block portion 24 for admitting coolant therethrough to exertpressure against circular flexible diaphragm 42 flexing it to close thenormally open contacts 44 making an electrical circuit at a pressuredetermined by spring 42*. One of the contacts 44 is electricallygrounded to the engine block 24 and thus connected to the grounded sideof battery 46. The other contact is connected to insulated terminal 44which in turn is connected to one side of gear shift operated normallyopen switch 36, the other side of which is connected to the battery 46through a small current limiting resistance. From this it is seen thatboth switches 36 and 38 must close conjunctively to ground the circuitbetween the battery 46 and the coil 54 to make the ignition system 28ineffective.

A timing cam 48 opens and closes the breaker points 50 in synchronismwith the drive shaft 14 rotation to,

provide timed spark. The ignition primary circuit connects the battery46 through closed points 50 and coil 54. When points 50 open thecapacitor 52 charges rapidly through the primary winding of the ignitiontransformer or coil 54 to provide the spark producing electric currentin the coil secondary winding to plug 30 and 31 through the usualignition distributor 55.

The switch 38 actuates at a pressure slightly above the desired highestidling engine speed and it being in conjunctive electrical ignitioncontrol circuit relation with the gear shift actuated switch 36 toobviate the two-cycle engine idling runaway condition as well asproviding an absolute maximum idling speed.

Alternately normally closed parallel connected pressure and gear shiftresponsive ignition conjunctively controlling switches may be seriesconnected between the battery 46 and the coil 54. As shown in FIG. 2Athe normally closed parallel connected switches 36C and 38C connect thebattery 46 to the ignition primary circuit portion including coil 54primary winding and points 50 to ground as indicated by the FIG. 2Aarrows. To make the ignition system ineffective by breaking the primaryignition circuit both switches 36C and 38C are simultaneously opened;the switch 36C being opened by moving the gear shift to neutral and theswitch 38C being opened by the water coolant pressure indicating a speedexceeding the predetermined maximum engine idling speed.

It is understood that where individual battery operated ignition systemsare provided that the just described embodiments may be utilized byconnecting the ignition coils of each system to switch 36 as coil 54 isconnected. Also the selection of the ground point in the primaryignition circuit is arbitrary and it may be made at any convenientcircuit junction.

FIGS. 3 and 4 illustrate two embodiments of this invention for use withtwo-cycle engines having a separate ignition system for each cylinderand where the ignition is short circuited to make it ineffective. InFIG. 3 there is a magneto generator having separate spark currentgenerating circuits 56 and 57 each including a magneto spark coil 60 andignition capacitor 62 with the coil secondaries being connected to thespark plugs 30 and 31. The breaker points 58 are actuated by engine 12to provide synchronized ignition to the plugs 3031 in the usual manner.

To make ignition systems ineffective by shorting a normally open switchor series connected normally open switches are connected in parallelcircuit relation to each primary winding 60 In the FIG. 3 illustrationtwo separate series switch elements in conjunctive controlling relationare required to make both ignition systems ineffective thereforeswitches 36 and 38' are constructed with normally open double polesingle throw switch elements 36, 36 38 and 38 and connected acrossprimaries 60 as shown in FIG. 3. When the gear shift 32 is in neutral,closing switch 36', and the engine speed has created sufiicient coolantpressure to close switch 38' it is seen that the primaries are shortcircuited thereby providing no ignition current to plugs 30 and 31.Alternately only one ignition system need be short circuited withequally effective, results to prevent idling speed runaway and toprovide an absolute no-load engine speed greater than the speedindicated by the coolant pressure.

FIG. 4 illustrates this invention applied to magneto operated individualcylinder ignition systems wherein shorting the ignition coil primarythrough the non-firing points makes the ignition system ineffective.This latter embodiment is preferred for ignition systems wherein thetiming cam is designed such that the non-firing points are closed at thetime the firing points open. Magneto coils 66 and 67 provide sparkcurrent in the usual manner respectively when the timed breaker points64 and 65 break. The timing arrangement is such that points 64 areclosed when points 65 are breaking to provide the spark to plug 31, andvice versa. Switches 36" and 38", actuated as heretofore described forthe switches 36 and 38, are series connected between the coil side ofthe points 64 and 65 for limiting the engine idling speed. When theswitches are closed and either of the points break to provide spark therespective ignition system is grounded through the non-firing or otherpoints, thereby providing grounding of separate ignition systems througha pair of singlepole single through throw switches.

It is understood that suitable modification may be made in the structureas disclosed, provided such modifications come within the spirit andscope of the appended claims. Having now therefore fully illustrated anddescribed my invention, what I claim to be new and desire to protect byLetters Patent is:

1. In an outboard motor having a two-cycle engine, a gear shift meanshaving a neutral position, an ignition system, an engine cooling systemincluding a coolant pump operatively connected to the engine forcreating a coolant pressure related to engine speed, a pressureresponsive switch operatively connected to said system for actuating ata predetermined coolant pressure, switch means operatively connected tothe shift means for actuation when said gear shift means is in a neutralposition, said pressure responsive switch and said switch means beingelectrically connected in conjunctive controlling circuit relation tothe ignition system for making the ignition ineffective when saidpressure responsive switch and said switch means have been actuated.

2. For limiting the no-load two-cycle engine idling speed of an outboardmotor, a battery, a battery operated ignition system including a primarycircuit, the improvement comprising a gear shift controlled normallyclosed switch indicating a neutral gear shift position when open, meansin the engine providing a fluid pressure related to engine speed, apressure sensitive switch operatively connected to said pressure meansfor opening at a predetermined pressure, and the said switches beingconnected in a parallel circuit which is series connected in the primarycircuit for making the ignition ineffective when both switches haveopened.

3. In an outboard motor having a two-cycle engine, a gear shift having aneutral position wherein the engine is operating under a no-loadcondition, an engine cooling system having coolant pressures related toenginespeed, an electrical ignition system having a primary circuitincluding an ignition coil with a primary winding, and normally openswitch means connected across the primary for short circuiting theprimary winding and being responsive to a coolant system pressureindicative of an engine speed greater than a predetermined engine idlingspeed and which is concurrent with the gear shift being in a neutralposition.

4. In an outboard motor having a two-cycle engine, a gear shift having aneutral position wherein the engine is operating under a no-loadcondition, an electrical ignition system having a primary circuitincluding an ignition coil primary winding, means in the engineproviding a fluid pressure related to engine speed, a pressureresponsive switch operatively connected to said means for closing at apredetermined pressure, a normally opened switch operatively connectedto the gear shift to close when the gear shift is in the neutralposition, and the said switches being connected in series across theprimary winding for making the ignition system ineffective under no-loadcondition at a predetermined engine speed.

5. In an outboard motor having a two-cycle engine, a gear shift having aneutral position wherein the engine is operating under a no-loadcondition, an engine cooling system having coolant pressures related toengine speed, a timing cam, an electrical ignition system having twosets of breaker points each having one ungrounded contact and beingoperatively associated with the timing cam such that one set is closedwhen the other set is opening for firing, a normally open pressureresponsive switch operatively connected to the coolant system andresponsive to a predetermined pressure therein for closing, a normallyopen switch operatively connected to the gear shift for closing when theshift is in neutral, and the switches being series connected between theungrounded contacts.

6. For limiting the no-load speed of a two-cycle engine, an enginecoolant system developing pressures related to engine speed, a gearshift having a neutral position wherein the engine is in a no-loadcondition, an electrical ignition system having a primary circuit with aportion including an ignition coil primary, normally open switch meanselectrically connected in parallel with said primary circuit portion andbeing operatively connected to the coolant system and to the gear shift,and the means being responsive to coolant system pressures exceeding apredetermined pressure and to the gear shift being in neutral forclosing to make the ignition system ineffective by shorting said circuitportion.

7. For limiting the no-load speed of a tWo-cycle engine, an enginecoolant system developing pressures related to engine speed, a gearshift having a netural position wherein the engine is in a no-loadcondition, an electrical ignition system having a primary circuit,normally closed switch means electrically connected in series with theprimary ignition circuit and being operatively References Cited in thefile of this patent UNITED STATES PATENTS 1,771,866 Stevenson et a1 July29, 1930 2,034,233 Hasselbaum Mar. 17, 1936 2,131,264 Benjamin Sept. 27,1938 2,762,235 Olson et a1. Sept. 11, 1956

